Sync largest-series-product docs with problem-specifications (#617)

* Sync largest-series-product docs with problem-specifications

The largest-series-product exercise has been overhauled as part of a project
to make practice exercises more consistent and friendly.

For more context, please see the discussion in the forum, as well as
the pull request that updated the exercise in the problem-specifications
repository:

- https://forum.exercism.org/t/new-project-making-practice-exercises-more-consistent-and-human-across-exercism/3943
- exercism/problem-specifications#2246

* Delete test cases from largest-series-product

This deletes two deprecated test cases so that we can
dramatically simplify the instructions for this exercise.

Author: kytrinyx

exercises/practice/largest-series-product/.docs/instructions.md

@@ -1,14 +1,26 @@
 # Instructions
 
-Given a string of digits, calculate the largest product for a contiguous substring of digits of length n.
+Your task is to look for patterns in the long sequence of digits in the encrypted signal.
 
-For example, for the input `'1027839564'`, the largest product for a series of 3 digits is 270 `(9 * 5 * 6)`, and the largest product for a series of 5 digits is 7560 `(7 * 8 * 3 * 9 * 5)`.
+The technique you're going to use here is called the largest series product.
 
-Note that these series are only required to occupy *adjacent positions* in the input; the digits need not be *numerically consecutive*.
+Let's define a few terms, first.
 
-For the input `'73167176531330624919225119674426574742355349194934'`,
-the largest product for a series of 6 digits is 23520.
+- **input**: the sequence of digits that you need to analyze
+- **series**: a sequence of adjacent digits (those that are next to each other) that is contained within the input
+- **span**: how many digits long each series is
+- **product**: what you get when you multiply numbers together
 
-For a series of zero digits, the largest product is 1 because 1 is the multiplicative identity.
-(You don't need to know what a multiplicative identity is to solve this problem;
-it just means that multiplying a number by 1 gives you the same number.)
+Let's work through an example, with the input `"63915"`.
+
+- To form a series, take adjacent digits in the original input.
+- If you are working with a span of `3`, there will be three possible series:
+  - `"639"`
+  - `"391"`
+  - `"915"`
+- Then we need to calculate the product of each series:
+  - The product of the series `"639"` is 162 (`6 × 3 × 9 = 162`)
+  - The product of the series `"391"` is 27 (`3 × 9 × 1 = 27`)
+  - The product of the series `"915"` is 45 (`9 × 1 × 5 = 45`)
+- 162 is bigger than both 27 and 45, so the largest series product of `"63915"` is from the series `"639"`.
+  So the answer is **162**.

exercises/practice/largest-series-product/.docs/introduction.md

@@ -0,0 +1,5 @@
+# Introduction
+
+You work for a government agency that has intercepted a series of encrypted communication signals from a group of bank robbers.
+The signals contain a long sequence of digits.
+Your team needs to use various digital signal processing techniques to analyze the signals and identify any patterns that may indicate the planning of a heist.

exercises/practice/largest-series-product/.meta/tests.toml

@@ -41,9 +41,11 @@ description = "rejects span longer than string length"
 
 [06bc8b90-0c51-4c54-ac22-3ec3893a079e]
 description = "reports 1 for empty string and empty product (0 span)"
+include = false
 
 [3ec0d92e-f2e2-4090-a380-70afee02f4c0]
 description = "reports 1 for nonempty string and empty product (0 span)"
+include = false
 
 [6d96c691-4374-4404-80ee-2ea8f3613dd4]
 description = "rejects empty string and nonzero span"

exercises/practice/largest-series-product/Tests/LargestSeriesProductTests/LargestSeriesProductTests.swift

@@ -53,14 +53,6 @@ class LargestSeriesProductTests: XCTestCase {
         }
     }
 
-    func testReports1ForEmptyStringAndEmptyProduct0Span() {
-        XCTAssertEqual(1, try? NumberSeries("").largestProduct(0))
-    }
-
-    func testReports1ForNonemptyStringAndEmptyProduct0Span() {
-        XCTAssertEqual(1, try? NumberSeries("123").largestProduct(0))
-    }
-
     func testRejectsEmptyStringAndNonzeroSpan() {
         XCTAssertThrowsError(_ = try NumberSeries("").largestProduct(1)) { error in
             XCTAssertEqual(error as? NumberSeries.NumberSeriesError, .spanLongerThanStringLength)